The invention was developed for the determination of the flow properties of finely granular solid materials, i.e. powders, and will be described further in relation to this field of application. However, the invention is not at all restricted to granular materials of a given degree of fineness and for those skilled in art it will be quite obvious that the invention is also applicable to coarser granular materials, provided a sample holder can be prepared, through which these materials may pass under the same conditions as in technological devices conventionally applied for passing materials with coarser grains.
In all professional fields interested in powder-technology, in particular in the pharmaceutical industry and among others in the course of producing plant protecting agents, fodder, foodstuff, cosmetics and household goods, determination of flow properties of granular powders and influencing same by technological means is of utmost importance, in order to optimize transport, charging and compressing of powders and similar operations and processes, as well as to ensure proper quality of products.
Various powder flow measuring systems have been considered and several methods are known; however, neither a test method, nor an apparatus is known, which would enable determination of all parameters influencing flow properties and a control of process (technological optimalization) based on said properties. The known solutions are suitable for determination of only one part of the important characteristics determining altogether the process, and only this part can be considered for the controlling parameters. Accordingly by using the devices corresponding to the state of art, satisfactory optimization can be achieved only on the basis of empirical information.
The velocity of flow of certain powdery products discharged from a given tank has been examined thoroughly, however, only in dependence upon some important parameters. R. L. Brown and J. C. Richards (Trans. Inst. Chem. Eng. 38, 243; 1960) examined the role of the grain size of the powder and the diameter of the discharge aperture, taking into consideration the density of the grain too, but the empirical mathematical correlation explored by them contained more constants of unknown nature than the considered known parameters. This correlation can be applied in practice only with severe limitations.
Of the parameters influencing outflow velocity of powders the effects of the following different parameters were examined:
the effect of the height of the powder column and grain size (F. Q. Danish and E. L. Parrot: J. Pharm. Sci. 60, 548, 1971.);
effect of moisture content (D. J. Craik and B. F. Miller: J. Pharm. Pharmac. 10, 136T; 1958);
effect of grain size distribution and the diameter of the aperture, T. M. Jones and N. Pilpel: J. Pharm. Pharmac. 18, 429; 1966;
the minimal diameter required for outflow, the effect of grain size, grain density and geometry of grain shape, K. Kurihara, I. Ichikawa: Chem. Pharm. Bull. 21, 394; 1973.
All of these examinations were performed with equipment which was provided with a powder tank with a discharge opening having changeable diameter (generally the change does not mean any optional change of the aperture diameter within a fixed range, but switching over between the closed and open state, independently of whether closing and opening could be performed for one single value of the diameter or with the exchangeability of the structural element containing the discharge aperture according to a size order). We shall use the definition "it can be opened and closed" instead of the attribute "changeable." In the course of measuring a so-called "Flowometer" was used, which was provided with an agitator, as well as an instrument suitable for measuring the shearing force. All these devices are suitable for determining only one group of the parameters to be considered and to define the empirical correlations between said preferential parameters.
From our earlier Hungarian Patent HU-PS No. 174 116 a solution is known which ensures advantageous apparatus or technical conditions for the determination of flow properties of solid granular materials with the simultaneous observation of different characteristics; this approach enables the application of a process, comprising keeping two characteristics out of three always constant and measuring the third parameter as an independent variable. The data obtained from the mass of facts by mathematical analysis are suitable for the determination of the data serving as a starting point for the optimization of production or processing. This technique enables an analysis only starting from variables of restricted number.